The disclosures herein relate generally to Advanced Configuration and Power Interface (“ACPI”)-compliant Peripheral Component Interface (“PCI”) devices and more particularly to an automatic power supply selector for such devices.
In early 1997, Intel Corporation, Microsoft Corporation, and Toshiba America Information Systems Inc. published an open specification to bring easy, flexible power management to a broad array of personal computer (“PC”) products, including servers, business systems, and desktop and portable computers. The new specification, known as the Advanced Configuration and Power Interface Specification (“ACPI”) version 1.0, enables PCS to come on instantly when accessed by a user and to remain available to perform automated tasks after they are turned off. ACPI enhances power management in PCS to provide a low-power sleep state that can be used instead of turning the PC off. ACPI also enables PCS to turn on and off peripherals such as CD-ROMs, network cards, hard disk drives and printers, as well as consumer electronics connected to a PC, such as VCRs, TVS, phones and stereos. Using ACPI, connected devices in turn will be able to activate the PC, making it easier for users to perform automated tasks and to integrate PCS into home communications and entertainment centers.
At least one type of motherboard produced by a well-known PC manufacturer does not support ACPI, but does provide a +3.3 volt power supply at a Vaux pin of each PCI adapter slot for connecting PCI devices to a PCI bus thereof, in addition to main power supply pins, defined as Vcc. The Vaux pin is defined as pin A14 in the PCI Local Bus Specification, PCI Special Interest Group, Rev. 2.1 (1995) (hereinafter “PCI 2.1 specification”), which is hereby incorporated by reference in its entirety. The Vaux pin along with a control pin A19, which is defined as PME#, are required for designs whether they are ACPI-compliant or not.
An extreme case, which should be supported by every motherboard, is where both Vaux and Vcc are supplied to a PCI device. In this case, the two power supplies should never be connected together.
Therefore, what is needed is a device for automatically switching between available power supply voltages depending upon the presence or absence of an auxiliary power supply.